1. Field of the Invention
The present invention relates to serial printers, and, more particularly, to a carriage drive system for a serial printer.
2. Description of the Related Art
Printers with carriage drive systems ("serial printers") are of a type that drive a printhead driver or firing mechanism ("printhead") which is generally attached to a frame mechanism, called a carriage or carrier, which moves the printhead back and forth at a given distance from the print media while printing takes place. An ink jet printer is an example of such a serial printer. Carriage drive systems suffer from a number of cyclical disturbances which cause velocity fluctuations during printing. These velocity fluctuations, in turn, cause print registration errors in the final output of the printer. Any system that moves a carriage at a given steady-state velocity will generate disturbances at given, repeatable spatial frequencies in addition to general noise. An example unit would be cycles per inch or cycles per millimeter.
In order to increase the quality of the final print, an attempt is made to drive the carriage in a perfectly smooth manner, with no changes to yaw, pitch, or roll of the carriage assembly while printing. If there are any disturbances introduced into the system, additional, non-ideal error velocity components can be introduced to the printhead, resulting in print registration errors in the final print on the output media. Some specific frequencies that are often a problem are the motor pole and commutation frequencies, timing belt tooth disturbances, and gear or pulley tooth disturbances from any gear or pulley systems in the drive train.
One approach to dealing with these disturbances is to change the system mechanically to dampen out the disturbances affecting the carriage, or otherwise attenuate the disturbances until the system is able to achieve its print registration accuracy requirements. This could take the form of better quality components which create less disturbance, altering the characteristics of the carriage, carriage drive belt, etc., to attenuate the disturbances, or some other such scheme. Alternately, sensors could be used to determine what the disturbances are in real time and adjust the print firings to compensate for them. A problem with all of these known approaches is that they add cost to the printer and/or are detrimental to other aspects of printer performance.
What is needed in the art is a method of improving print registration which does not add to the cost of the printer and does not degrade printer performance.